The present invention relates to a method of reducing the density of silicone foam resulting from the platinum-catalyzed generation of hydrogen as. More particularly, the present invention relates to a method for making silicone foam at a reduced density by cooling the foam components prior to mixing to a temperature of up to 5.degree. C. and thereafter maintaining the foamable mixture at a reduced temperature.
Elastomeric silicone foams have been used in a variety of applications such as thermo- and electricalinsulators, foam barriers, and cushions. Even though elastomeric silicone foams are superior to organic foams in many instances, organic foams are often used based on economic consideration.
At the present time, commercially available silicone foam has a foam density which can provide a 15-25 pound/cubic ft. foam structure. One method of reducing the cost of elastomeric silicone foam, is to reduce foam density without altering the desirable physical properties of the foam material.
Although silicone foam may be made by using a blowing agent, or even mechanical mixing, another technique is by effecting the generation of hydrogen gas using a platinum catalyst as shown by Smith, U.S. Pat. No. 3,923,705. Elastomeric silicone foams can be made by forming a mixture of a silanol, a silicone hydride, and a vinyl-containing silicone in the presence of a platinum catalyst. There is effected the simultaneous generation of hydrogen gas along with cross-linking. For example, Modic, U.S. Pat. No. 4,189,545, incorporated herein by reference produces silicone foam by adding water to a composition of a vinyl-containing siloxane, a hydride-containing siloxane and platinum to generate hydrogen simultaneously with cross-linking. Modic, U.S. Pat. No. 4,418,157 shows the strengthening of silicone foam by adding a resinous copolymer, while Bauman et al., U.S. Pat. No. 4,599,367 reduces silicone foam density by using a combination of silanol and water.
The present invention is based on the discovery that a substantial reduction in silicone foam density can be achieved, if the silicon foam components are initially cooled prior to mixing. The resulting foamable mixture, upon blending of the components, also can be cooled to provide a significant density reduction.